My car has alot of electronics in it, and ive replaced alternators with brand new ones, batteries, whatever i do, added extra grounds everything, and no matter what my voltage always stays at like 12.5 volts not the 14 or so i should have. so the problem is that this directly affects the fuel pressure when the voltage is lower. It can cause a big pressure loss as the volts go between 11.5 and 12.5 volts . Im putting the car back together right now and adding a dual b attery to the trunk.
Do you think This is goiong to be enough for me? this alternator is huge and it has never died or anything like that but its just not enough volts.
Ive heard of wiring the fuel pump directly to the alternator would this help me too?

When i first start my car and start driving my fuel pressure is at 60lbs thats where i got the best dyno run from it. when i floor it it drops down to 45 lbs, but when my voltage is low i can go down to 30lbs at WOT.

 

True, your vehicle voltage when the car is running should be upwards of 14 volts. This is determined by the alternator (a huge current draw on the system may also affect battery voltage, but under "normal" conditions, this shouldn't happen). Have you removed the aftermarket electronics from the the car to check how they affect the car's charging system. This seems the easiest way to determine what is at fault. Also, have you had the alternator bench tested to determine if it is operating correctly? Have you changed pulley sizes on the alternator and/or crankshaft?

Adding a dual battery set-up to the vehicle will not increase the system's running voltage, but it will increase the cranking amps when starting the car (if the 2 batteries are wired in parallel and obviously you would not connect them in series as you would then supply 24 volts to the car) Wiring the fuel pump positive wire directly to the output terminal of the alternator will help to supply the f.p. with the highest voltage possible, but it sounds like you have a bigger problem. What is the voltage output of the alternator at 2500-3000 rpms with all the electronic shut off? Measure this with a voltmeter positive lead connected to the alt. and the voltmeter's negative lead connected to the engine block.

I'm presuming this is an LT-X motor based on your user name, so I would have to question your fuel pump pressure as well. It is about 15 lbs. higher than it should be. With the vacuum line removed from the FPR, at an idle, the fuel pressure should be at 43.5 lbs. Is there more we should know???

 

It has an aeromotive regulator and the reason i cranked it up so high was because its the only way i got the car to run right on the dyno, i had to crank the fuel pressure because it was wayy too lean .Im going to be starting the car back up today i just had the engine out for some other maintenance things and oil pump, ill post more info once i get it running and dig into the fuel pressure / voltage problem.

 

Assuming you have a 93-97 Camaro from your user name. Where are you getting your voltage readings from? They are very similar to the ones i get from my datalogs. The fuel pressure is a big problem and needs to be fixed right. I found this part and will help with the voltage issues at wot. http://store.summitracing.com/partde...59098+%2D42536
Im guessing you have a fuel pump issue not supplying enough fuel which could be the pump or a dirty fuel filter. You should put a signature for your car so we will know the type car you have and whats been done to it. If you turn off all the extra draws or disconnect them you can see if they are causing any voltage drop. From reading all the threads over the past year i would guess your voltage is more common for these cars than the 14 volts you think you should be seeing. Ive had voltage as low as 11.5 and my fuel pressure would be reading correctly at that time.

 

mrmint69:
Not to hijack the thread but that Casper's product looks like useful insurance ... are there any known downsides to using this on the street?

 

Another alternative:

http://www.kennebell.net/accessories...boostapump.htm

One thing to keep in mind... voltage affects both the fuel pump and the injectors. The injectors should have the proper offsets programmed into the PCM to correct for the actual system voltage. Are you sure you have the right programming for the injectors? Forcing the injectors to flow 15% extra fuel with the higher fuel pressure is not the way to solve the problem, if the PCM injector constant is still based on 43.5psi flow rates.

 

Injuneer:
Ooops ... (anticipating brain-fade!) I knew it would be a good idea to ask.
I mistakenly thought the voltage increase was only to the fuel pump to ensure maximum output and that the FMUs would modulate it properly. I forgot about the injectors!

 

I think he needs to find out why his system volts are so low, before he does anything. In all the data logs I've reviewed for people, most of them are in the high 12V's to low 13V's at WOT. I don't think I've ever been sent a log with the system as high as 14V. But 11.5V would definitely be a sign of a system that can't keep up with the required amps.

I'm going to make another suggestion I've made several times.... add a "signature" with basic info about your car - year, model, engine, tranny, major mods, etc. People are just guessing or assuming that you have an LTx 4th Gen, based on your screen name. But there are many people here whose screen names are completely different than the car they actually own.

 

I just got the car all running properly, i removed all my electronics right now for the time being. I checked voltage right on the alternator and its 14.0 with or without both cooling fans on, so thats no problem.

I just picked up my 2 gauge wire to run to the trunk for the second battery , should i run it through the car or underneath?

Once i get it aligned monday ill take it out and see how the pressure is at wot.
Im sure its gonna do what it always has though and drop down to near 30lbs at wot.

 

On the street? none really... it doesn't do anything until TPS ~70% (63% on the one I received from summit).

Speed Secrets tracked down a miss at 5500rpms that was messing with my 396 build-up. After a few runs while logging, they found the TPS reading dumped to 0% once the boost came on. Sure, the car ran for a while past booster activation, but it topped out at 5500rpms when it wouldn't enter PE mode (MAF-mode alone just didn't fuel it enough apparently). The system voltage went from 13.6v to 15.6v when activated, and instantly the TPS tanked.

Strangely, it doesn't throw a code when this happens since the PCM won't do that until ~16.5v... even though 15+volts seems to cause problems.

While a higher system voltage may be ok for ignition, fuel pumps, and head lights... the TPS crap out, and loss of PE is a great reason to avoid system-wide voltages of 15 or higher. Low 14's seem fine (I get 14.2v at startup on a cold day).

Solution: If you've already upgraded your battery ground and alternator-battery (+) wire, and a hot-wire upgrade to the fuel pump (a la racetronix or similar), you should look at device specific solutions like Fred's boost-a-pump example. Going system-wide just isn't worth it.

This might be a good add-on for stereo guys if they have a separate alternator for a hugh system (feed 15+volts directly to an amp), but pluggin this thing into your only alternator which runs the PCM and all engine sensors just isn't worth it.

Thanks to Speed Secrets for their help with my headache.